sync readme hello_world.py example with actual implementation
sync readme hello_world.py example with actual implementation

Signed-off-by: Yonghong Song <e76892bbe783db2f627de1232e139db4de43da60@plumgrid.com>

shodoco/bcc,arslanabbasi/bcc,bpowers/bcc,brendangregg/bcc,mkacik/bcc,mkacik/bcc,iovisor/bcc,iovisor/bcc,mcaleavya/bcc,mcaleavya/bcc,shodoco/bcc,tuxology/bcc,mbudiu-bfn/bcc,romain-intel/bcc,shodoco/bcc,zaafar/bcc,brendangregg/bcc,bpowers/bcc,arslanabbasi/bcc,zaafar/bcc,arslanabbasi/bcc,bpowers/bcc,mkacik/bcc,bpowers/bcc,tuxology/bcc,shodoco/bcc,zaafar/bcc,zaafar/bcc,tuxology/bcc,mcaleavya/bcc,tuxology/bcc,mcaleavya/bcc,tuxology/bcc,arslanabbasi/bcc,romain-intel/bcc,brendangregg/bcc,mbudiu-bfn/bcc,iovisor/bcc,iovisor/bcc,mcaleavya/bcc,mkacik/bcc,romain-intel/bcc,romain-intel/bcc,mbudiu-bfn/bcc,iovisor/bcc,mkacik/bcc,bpowers/bcc,mbudiu-bfn/bcc,brendangregg/bcc,shodoco/bcc,brendangregg/bcc,mbudiu-bfn/bcc,zaafar/bcc,arslanabbasi/bcc,romain-intel/bcc